Methods and devices for spinal fixation element placement

ABSTRACT

Minimally invasive methods and devices are provided for positioning a spinal fixation element in relation to adjacent spinal anchors. In an exemplary embodiment, the device is a percutaneous access device that can be coupled to a spinal anchor, and the method includes the step of positioning a spinal fixation element through at least one sidewall opening of at least two percutaneous access devices such that the spinal fixation element extends in a lengthwise orientation that is substantially transverse to the longitudinal axis of each percutaneous access device. The spinal fixation element can then be advanced in the lengthwise orientation to seat the spinal fixation element in or adjacent to the receiver heads of at least two adjacent spinal anchors. A fastening element or other closure mechanism can then be applied to each spinal anchor to engage the spinal fixation element within the receiver heads of the adjacent anchors.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.10/737,537 filed on Dec. 16, 2003 and entitled “Methods and Devices forSpinal Fixation Element Placement,” which is hereby incorporated byreference in its entirety.

FIELD OF THE INVENTION

This application relates to tools for use in spinal surgery, and inparticular to minimally invasive methods and devices for introducing aspinal fixation element to one or more spinal anchor sites within apatient's spine.

BACKGROUND OF THE INVENTION

For a number of known reasons, spinal fixation devices are used inorthopedic surgery to align and/or fix a desired relationship betweenadjacent vertebral bodies. Such devices typically include a spinalfixation element, such as a relatively rigid fixation rod, that iscoupled to adjacent vertebrae by attaching the element to variousanchoring devices, such as hooks, bolts, wires, or screws. The fixationelements can have a predetermined contour that has been designedaccording to the properties of the target implantation site, and onceinstalled, the instrument holds the vertebrae in a desired spatialrelationship, either until desired healing or spinal fusion has takenplace, or for some longer period of time.

Spinal fixation elements can be anchored to specific portions of thevertebrae. Since each vertebra varies in shape and size, a variety ofanchoring devices have been developed to facilitate engagement of aparticular portion of the bone. Pedicle screw assemblies, for example,have a shape and size that is configured to engage pedicle bone. Suchscrews typically include a threaded shank that is adapted to be threadedinto a vertebra, and a head portion having a rod-receiving element,usually in the form of a U-shaped slot formed in the head. A set-screw,plug, or similar type of fastening mechanism is used to lock thefixation element, e.g., a spinal rod, into the rod-receiving head of thepedicle screw. In use, the shank portion of each screw is threaded intoa vertebra, and once properly positioned, a rod is seated through therod-receiving member of each screw and the rod is locked in place bytightening a cap or other fastener mechanism to securely interconnecteach screw and the fixation rod.

Recently, the trend in spinal surgery has been moving toward providingminimally invasive devices and methods for implanting spinal fixationdevices. One such method, for example, is disclosed in U.S. Pat. No.6,530,929 of Justis et al. and it utilizes two percutaneous accessdevices for implanting an anchoring device, such as a spinal screw, intoadjacent vertebrae. A spinal rod is then introduced through a thirdincision a distance apart from the percutaneous access sites, and therod is transversely moved into the rod-engaging portion of each spinalscrew. The percutaneous access devices can then be used to apply closuremechanisms to the rod-engaging heads to lock the rod therein. While thisprocedure offers advantages over prior art invasive techniques, thetransverse introduction of the rod can cause significant damage tosurrounding tissue and muscle. Moreover, the use of three separateaccess sites can undesirably lengthen the surgical procedure, andincrease patient trauma and recovery time.

Accordingly, there remains a need for improved minimally invasivedevices and methods for introducing a spinal fixation element into apatient's spine.

SUMMARY OF THE INVENTION

The present invention generally provides methods for introducing aspinal fixation element into a receiver head of adjacent spinal anchors.In one embodiment, the method utilizes at least two percutaneous accessdevices, each of which has a proximal end positioned outside a patient'sbody and a distal end coupled to a spinal anchor. The access devicepreferably includes at least one sidewall opening extending from thedistal end through at least a portion of the percutaneous access device.In use, a spinal fixation element is positioned through the sidewallopening(s) in at least two adjacent percutaneous access devices suchthat the spinal fixation element extends in an orientation that issubstantially transverse to a longitudinal axis of each percutaneousaccess device. The spinal fixation element is then advanced in thesubstantially transverse orientation to seat the spinal fixation elementin or adjacent to the receiver head of at least two spinal anchors thatare preferably implanted within adjacent vertebrae.

In an exemplary embodiment, each percutaneous access device includesfirst and second opposed sidewall openings, and at least one of thefirst and second sidewall openings extends from the distal end andterminates at a position distal to the proximal end. The percutaneousaccess devices can also optionally include a cannula, sleeve, or similardevice disposed therearound that is effective to prevent removal of eachpercutaneous device from the spinal anchor coupled thereto. The sleevepreferably includes at least one sidewall opening formed therein that isadapted to align with the at least one sidewall opening in thepercutaneous access device.

In another embodiment of the present invention, a percutaneous accesssystem for introducing a spinal fixation element into a patient's bodyis provided. The system includes at least two spinal anchors that areadapted to be disposed in bone, at least one elongate, generallycylindrical hollow tube having at least one sidewall opening extendingfrom the distal end thereof and terminating at a position distal to theproximal end, and a spinal fixation element. The system can also includeat least one sleeve which is adapted to be slidably disposed around atleast a portion of one of the hollow tubes. The sleeve(s) preferablyincludes at least one sidewall opening formed therein that is adapted toalign with the sidewall opening(s) formed in the hollow tube. The systemcan also include a driver mechanism having a proximal handle portion,and a distal end that is adapted to couple to a spinal anchor such thatrotation of the driver mechanism is effective to thread the spinalanchor into bone. The driver mechanism is preferably adapted to bedisposed through the hollow tube(s).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a percutaneous access device coupled toa spinal anchor according to one embodiment of the present invention;

FIG. 2 is a cross-sectional view taken along the longitudinal axis L ofthe percutaneous access device shown in FIG. 1;

FIG. 3A is a posterior view of a midline incision formed in thethoracolumbar fascia of a patient's back;

FIG. 3B is an end view showing a blunt dissection of the musclessurrounding a patient's vertebra;

FIG. 4 is an end view of the vertebra shown in FIG. 3B showing atechnique for separating the muscles along the muscle plane to gainaccess to the vertebra;

FIG. 5 is an end view of the vertebra shown in FIG. 4 showing placementof a k-wire through the incision and into the patient's vertebra;

FIG. 6 is an end view of the vertebra shown in FIG. 5 having anobturator and several dilators disposed over the k-wire to dilate thetissue and muscles;

FIG. 7 is perspective view of a spinal anchor having a percutaneousaccess device coupled thereto and extending through an incision formedin the patient's tissue surface to implant the spinal anchor in avertebra;

FIG. 8 is a perspective view of two percutaneous access devices attachedto spinal anchors that are disposed within adjacent vertebrae in apatient's spinal column;

FIG. 9 illustrates a method for introducing a spinal fixation elementthrough the percutaneous access devices shown in FIG. 8;

FIG. 10 is a perspective view of the spinal fixation element shown inFIG. 9 being advanced toward the spinal anchors using a pusher device;

FIG. 11 is a perspective view of the spinal fixation element shown inFIG. 10 after it is fully positioned within receiver heads of theadjacent spinal anchors;

FIG. 12 is a perspective view of a compression tool positioned aroundthe percutaneous access devices shown in FIG. 11 and compressing thedevices toward one another; and

FIG. 13 is a perspective view of a closure mechanism being appliedthrough one of the percutaneous access devices to lock the spinalfixation element in relation to the spinal anchor.

DETAILED DESCRIPTION OF THE INVENTION

The present invention provides minimally invasive methods and devicesfor introducing a spinal fixation element into a surgical site in apatient's spinal column. In general, the method involves positioning aspinal fixation element through openings formed in at least two adjacentpercutaneous access devices such that the spinal fixation elementextends between the at least two adjacent percutaneous access devices ina lengthwise orientation. The spinal fixation element can then beadvanced in a distal direction to seat the spinal fixation element inthe receiver heads of the adjacent spinal anchors, or to otherwiseposition the spinal fixation element in relation to the adjacent spinalanchors. A fastening element or other closure mechanism can optionallybe applied to each spinal anchor to engage the spinal fixation elementwithin the receiver heads of the adjacent anchors, or to otherwisedirectly or indirectly connect the spinal fixation element to theanchors.

While a variety of devices can be used to perform the methods of thepresent invention, FIGS. 1 and 2 illustrate an exemplary embodiment of apercutaneous access device 12 that is mated to a spinal anchor 50 toform a spinal implant assembly 10. The device 12 is in the form of agenerally elongate, cylindrical tube having an inner lumen 12 c formedtherein and defining a longitudinal axis L that extends between proximaland distal ends 12 a, 12 b. The size of the access device 12 can varydepending on the intended use, but it should have a length l that allowsthe proximal end 12 a of the access device 12 to be positioned outsidethe patient's body, while the distal end 12 b of the access device 12 iscoupled to, or positioned adjacent to, a spinal anchor, e.g., anchor 50,that is disposed in a vertebra in a patient's spine. The inner diameterd_(i) of the access device 12 can also vary depending on the intendeduse, but the inner diameter d_(i) is preferably sufficient toaccommodate a diameter or width of a spinal fixation element to beintroduced therethrough.

The percutaneous access device 12 also preferably includes at least onesidewall opening or slot 14, and more preferably two opposed sidewallopenings (only one opening 14 is shown), formed therein and extendingproximally from the distal end 12 b thereof. The openings 14 allow aspinal fixation element to be positioned lengthwise between two adjacentdevices 12 such that the spinal fixation element extends in anorientation that is substantially transverse to the longitudinal axis Lof the access devices 12, i.e., that crosses the longitudinal axis L ofthe access devices 12. The exact position of the spinal fixation elementwith respect to the longitudinal axis L will of course vary depending onthe configuration of the spinal fixation element. The shape and size ofthe openings 14 can also vary depending on the configuration of thespinal fixation element, but the openings 14 preferably have a generallyelongate shape with a width w that is sufficient to accommodate thediameter of the spinal fixation element. The openings 14 preferablyextend over about half of the length, or more than half of the length,of the percutaneous access device 12. This allows a proximal portion ofeach opening 14 to be positioned outside a patient's body while thedevice 12 is in use, thus allowing a spinal fixation element to beexternally positioned through the openings 14 and then moved distally tobe implanted. A person skilled in the art will appreciate that thepercutaneous access device 12 can include any number of sidewallopenings having any shape that is sufficient to allow a spinal fixationelement to be positioned therethrough.

Continuing to refer to FIG. 1, in use, the percutaneous access device 12is preferably adapted to attach to a spinal anchor 50, and morepreferably to the receiver head 52 of a spinal anchor 50. Accordingly,the distal end 12 c of the percutaneous access device 12 can include oneor more mating elements 18 formed thereon or therein for engaging thespinal anchor 50. Suitable mating elements include, for example,threads, a twist-lock engagement, a snap-on engagement, or any othertechnique known in the art, and in an exemplary embodiment the matingelements are formed on opposed inner surfaces of the distal end 12 b ofthe access device 12. A sleeve (not shown) or other device, preferablyhaving sidewall openings that correspond with the sidewall openings 14formed in the percutaneous access device 12, can also be placed over thepercutaneous access device 12, and optionally over the anchor 50 aswell, to prevent disengagement of the access device 12 from the anchor50 during use. Exemplary techniques for mating the percutaneous accessdevice 12 to a spinal anchor are disclosed in a patent applicationentitled “Percutaneous Access Devices and Bone Anchor Assemblies,” filedconcurrently herewith. A person skilled in the art will appreciate thata variety of other techniques can be used to removably mate thepercutaneous access device to a spinal anchor.

Still referring to FIG. 1, an exemplary spinal anchor for use with themethods and devices of the present invention is shown. A person skilledin the art will appreciate that a variety of implants can be used withthe devices and methods of the present invention, including, forexample, spinal screws, hooks, bolts, and wires. By way of non-limitingexample, FIG. 1 illustrates a spinal screw 50 that includes a distal,bone-engaging portion, e.g., a threaded shank 54, and a proximal,U-shaped, receiver head 52 that is adapted to seat a spinal fixationelement, such as a spinal rod (not shown). The threaded shank 54 can befixedly attached to the receiver head 52 to form a monoaxial screw, oralternatively the shank 54 can be configured as a polyaxial screw, asshown, that is rotatably disposed through an opening formed in thedistal end of the receiver head 52 to allow rotation of the shank 54with respect to the receiver head 52. A variety of techniques can beused to allow rotation of the head 52 with respect to the shank 54.

FIGS. 3A-13 show a minimally invasive method of implanting a spinalfixation element into the receiver heads of adjacent spinal anchors.While the method is shown and described in connection with thepercutaneous access device 12 and spinal screw 50 disclosed herein, aperson skilled in the art will appreciate that the method is not limitedto use with such devices, and that a variety of other devices known inthe art can be used. Moreover, while only two access devices 12, 12′ andtwo implants 50, 50′ are shown in FIGS. 8-13, the method of the presentinvention can be performed using any number of access devices and spinalanchors. The method can also be performed using only some of the methodsteps disclosed herein, and/or using other methods known in the art.

The procedure preferably begins by forming an incision through thetissue located adjacent to the desired implant site. While the location,shape, and size of the incision will depend on the type and quantity ofspinal anchors being implanted, FIG. 3A illustrates a midline, bluntdissection incision 62 formed in the thoracolumbar fascia in thepatient's back along the muscle plane. The length of the incision 62 isabout 4-5 cm, however this can vary depending on the procedure. Once themidline incision 62 is formed, blunt finger dissection can be used, asshown in FIG. 4, to separate the longissimus thoracis and multifidusmuscles, thereby exposing the facet and the junction of the transverseprocess and superior articular process.

As shown in FIG. 5, a guide wire, e.g., a k-wire 64, can be implanted,either prior to or after formation of the incision, at each spinalanchor implant site. The k-wire 64 preferably extends between themuscles and into the vertebra at the desired entry point of the spinalanchor. Fluoroscopy is typically used to facilitate proper placement ofthe k-wire 64.

The opposed ends of the incision can then be dilated to provide apathway for delivery of a spinal anchor to each implant site. FIG. 6illustrates dilation at one end of the incision 62 using an obturator 66a having several dilators 66 b, 66 c of increasing size placed thereover. The dilators 66 b, 66 c are delivered over the obturator 66 a andk-wire 64 to essentially stretch the skin around the incision 62 and toexpand the pathway to the anchor site. While not illustrated, a personskilled in the art will appreciate that the incision 62 can optionallybe held opening using a refractor or an expandable cannula.

Once the incision 62 is dilated to the proper size, an anchor can bedelivered to each anchor site, as shown in FIG. 7. This proceduretypically involves preparation of the vertebra 60 using one or more bonepreparation instruments, such as drills, taps, awls, burrs, probes, etc.While not always necessary, one or more cannulae can be used to providea pathway from the incision 62 to the anchor site for insertion of thebone preparation instruments and/or the anchor. In an exemplaryembodiment, a relatively small cannula is used to introduce bonepreparation instruments into the surgical site. The incision 62 can thenbe further dilated, and the small cannula can be replaced with a largercannula that is adapted to receive or mate to the anchor.

Once the vertebra 60 is prepared, a spinal anchor can be implanted ateach implant site. An access device 12, 12′ can be mated to each anchor50, 50′ after insertion of the anchor 50, 50′ into bone 60, 60′, butmore preferably each percutaneous access device 12, 12′ is attached tothe anchor 50, 50′ prior to insertion of the anchor 50, 50′ into bone60, 60′ to provide a passageway for a driver tool for driving the anchor50 into bone 60, 60′. FIG. 7 illustrates anchor 50 implanted in a firstvertebra 60 and having access device 12 attached thereto. While notshown, the anchor 50 is preferably cannulated to allow the k-wire 64 toextend through the anchor 50 and the access device 12 to guide thedevices 50, 12 toward the implant site. FIG. 7 further illustrates asecond anchor 50′ having an access device 12′ mated thereto. As shown,the screw 50′ is about to be implanted in a second vertebra 60′ that isadjacent to the first vertebra 60. Once the screw 50′ is positionedadjacent to the vertebra 60′, a driver tool 200 can be positionedthrough the access device 12′ and coupled to the receiver head 52′ ofthe screw 50′ to drive the screw 50′ into the vertebra 60′.

In another embodiment, a sleeve can be placed over each access device12, 12′, either prior to or after the devices 12, 12′, 50, 50′ areimplanted, to prevent the devices 12, 12′ from becoming disengaged fromthe anchors 50, 50′ to which they are attached. The sleeve (not shown)is preferably in the form of a cannula that has substantially the sameconfiguration as each access device 12, 12′. The use of a sleeve isparticularly desirable where the access devices 12, 12′ utilize pinmembers that engage corresponding detents formed on an outer surface ofeach screw head 52, 52′, as the sleeve will prevent the pin members frombecoming disengaged from the detents. The sleeve can also optionallyserve as an access device, allowing access devices 12, 12′ to bedetached and removed from the anchors 50, 50′.

After the anchors are implanted, as shown in FIG. 8, a spinal fixationelement is delivered to the anchor sites. As shown in FIG. 9, the spinalfixation element 70 is positioned through the openings 14, 14′ in theadjacent devices 12, 12′ such that the spinal fixation element 70extends in a lengthwise orientation which is substantially transverse tothe longitudinal axis L of the access devices 12, 12′. The exact angleof the fixation element 70 with respect to the percutaneous accessdevices 12, 12′ will vary depending on the orientation of the accessdevice 12, 12′ with respect to the patient's spinal column, and it isunderstood that the orientation can vary during use since thepercutaneous access devices 12, 12′ can be oriented at various anglesthroughout the surgical procedure.

The spinal fixation element 70 is then moved distally toward the distalend 12 b, 12 b′ of the percutaneous access devices 12, 12′. As thespinal fixation element 70 moves distally, it will advantageously passbetween the muscles, thus eliminating the need to cut or tear tissue.The method is also particularly advantageous in that the percutaneousaccess devices 12, 12′ direct the spinal fixation element 70 into thereceiver heads 52, 52′ of the adjacent spinal anchors 50, 50′, thusallowing the spinal fixation element to be properly positioned withoutthe necessity for direct visual access to the surgical site.

Movement of the spinal fixation element 70 in the distal direction canbe achieved using pusher shaft 80, as shown in FIGS. 10 and 11. Thepusher shaft 80 can have a variety of configurations, but it should beeffective to allow controlled movement of the spinal fixation element70. A person skilled in the art will appreciate that a variety of othertechniques can be used to advance the spinal fixation element 70distally between the percutaneous access devices 12, 12′ to seat thespinal fixation element 70 into the receiver heads 52, 52′ of adjacentspinal anchors 50, 50′. In the illustrated embodiment, the pusher shaft80 includes a seating member 82 formed on a distal end thereof that isadapted to seat the spinal fixation element 70. The seating member 82,which is similar to a receiver head of a spinal anchor, is generallycylindrical and includes an open distal end with opposed U-shapedcut-out portions formed therein for receiving the spinal fixationelement 70. In use, the seating member 82 is positioned around thespinal fixation element 70 and a force is applied to the pusher shaft 80to move the spinal fixation element 70 distally.

Once the spinal fixation element 70 is fully seated in the receiverheads 52, 52′ of the adjacent spinal anchors 50, 50′, as shown in FIG.11, the pusher shaft 80, if used, can then be removed or detached fromthe spinal fixation element 70, and a closure mechanism can be appliedto one or both receiver heads 52, 52′ to retain the spinal fixationelement 70 therein. In an exemplary embodiment, however, a compressiontool 100 is used to compress the access devices 12, 12′ toward oneanother prior to applying a closure mechanism to each anchor 50, 50′.The closure mechanism(s) can, however, be partially applied beforecompression.

An exemplary compression tool 100 is shown in FIG. 12, and in general itincludes opposed arms 102, 104 that are pivotally coupled to one anotherat a substantial mid-point thereof such that each arm 102, 104 includesa distal portion 102 b, 104 b that is adapted to be disposed around apercutaneous access device 12, 12′, and a proximal, handle portion 102a, 104 a. The device 100 can also include a fulcrum (not shown) that isdisposed between the arms 102, 104 to facilitate controlled movement ofthe arms 102, 104 with respect to one another. In use, the distalportion 102 b, 104 b of each arm 102, 104 is placed around an accessdevice 12, 12′, preferably around the distal end 12 b, 12 b′ of eachdevice 12, 12′ and/or around the head 52, 52′ of each anchor 50, 50′.The proximal, handle portions 102 a, 104 a are then brought toward oneanother to move the access devices 12, 12′ toward one another,preferably while maintaining relative spacing therebetween, as shown inFIG. 12.

Once properly positioned, a closure mechanism can be applied, preferablyvia the access devices 12, 12′, to each anchor head 50, 50′ to retainthe spinal fixation element 70 within the receiver heads 52, 52′. Avariety of closure mechanisms and tools for delivering closuremechanisms are known in the art and they can be used with the presentinvention. By way of non-limiting example, FIG. 13 illustrates a drivertool 90 disposed through access device 12 for applying a closuremechanism, such as a set screw, to the receiver head 52 of the spinalanchor 50 to lock the spinal fixation element 70 with respect to thespinal anchor 50. This step can be repeated for the adjacent spinalanchor(s).

A person skilled in the art will appreciate that the spinal fixationelement 70 does not need to be directly attached to each anchor 50, 50′,and that it can be indirectly attached to the anchors 50, 50′ using, forexample, a band clamp, or slotted or offset connectors.

Once the fixation element 70 is secured in relation to the implants 50,50′, the access devices 12, 12′ can be removed (if attached) from theimplants 50, 50′, leaving only a single, relatively small incision inthe patient where each access device 12, 12′ and the spinal fixationelement 70 was introduced. This is particularly advantageous in that itreduces the amount of trauma caused to the patient, and it minimizes thedamage to muscle surrounding the surgical site.

As previously stated, a person skilled in the art will appreciate thatthe method can be performed in any sequence using any of the steps.Moreover, the access devices of the present invention can be used todeliver multiple spinal fixation elements simultaneously orsequentially, and/or to perform a variety of other surgical proceduresnot illustrated or described herein.

One skilled in the art will appreciate further features and advantagesof the invention based on the above-described embodiments. Accordingly,the invention is not to be limited by what has been particularly shownand described, except as indicated by the appended claims. Allpublications and references cited herein are expressly incorporatedherein by reference in their entirety.

1. A method for introducing a spinal fixation element into a patient'sspinal column, comprising: providing at least two percutaneous accessdevices, each device having a proximal end positioned outside apatient's body, a distal end coupled to a spinal anchor, a lumenextending between the proximal and distal ends of the percutaneousaccess device and defining a longitudinal axis, and at least onesidewall opening extending from the distal end through at least aportion of the percutaneous access device; positioning a spinal fixationelement through the at least one sidewall opening of at least twopercutaneous access devices such that the spinal fixation elementextends in an orientation substantially transverse to the longitudinalaxis of each percutaneous access device; and advancing the spinalfixation element in the substantially transverse orientation to seat thespinal fixation element in a receiver head of at least two adjacentspinal anchors.
 2. The method of claim 1, wherein each percutaneousaccess device includes first and second opposed sidewall openings. 3.The method of claim 1, wherein the at least one sidewall opening extendsfrom the distal end and terminates at a position distal to the proximalend.
 4. The method of claim 1, wherein each percutaneous access deviceincludes a sleeve disposed therearound and effective to prevent removalof each percutaneous device from the spinal anchor coupled thereto, thesleeve including at least one sidewall opening formed therein that isadapted to align with the at least one sidewall opening in thepercutaneous access device.
 5. The method of claim 1, wherein eachpercutaneous access device is threadably coupled to the receiver head ofeach spinal anchor.
 6. The method of claim 1, wherein each percutaneousaccess device and spinal anchor are mating together by a twist-lockclosure mechanism.
 7. The method of claim 1, wherein each percutaneousaccess device is coupled to the receiver head of a spinal anchor, andthe at least one opening in the percutaneous access device is adapted toalign with a seating portion formed in each receiver head.
 8. The methodof claim 1, further comprising providing a pusher mechanism adapted toadvance the spinal fixation element into the receiver head of adjacentspinal anchors.
 9. The method of claim 1, further comprising providing acompression tool, and engaging at least two adjacent percutaneous accessdevices to compress the devices toward one another while maintainingrelative spacing therebetween.
 10. The method of claim 9, wherein thecompression tool comprises first and second opposed arms that arepivotally mated to one another.
 11. The method of claim 1, furthercomprising delivering a closure mechanism through each percutaneousaccess device and applying the closure mechanism to each spinal anchorto lock the spinal fixation element in the receiver heads of theanchors.
 12. A method for introducing a spinal fixation element into areceiver head of adjacent spinal anchors, comprising: positioning aspinal fixation element through openings formed in at least two adjacentpercutaneous access devices such that the spinal fixation elementextends between the at least two adjacent percutaneous access devices ina lengthwise orientation; advancing the spinal fixation element in adistal direction to seat the spinal fixation element in the receiverheads of the adjacent spinal anchors.
 13. The method of claim 12,wherein the spinal fixation element is advanced between muscles.
 14. Themethod of claim 12, wherein the each spinal anchor is coupled to apercutaneous access device.
 15. The method of claim 12, wherein eachpercutaneous access device includes opposed openings formed therethroughand extending along a length thereof.
 16. The method of claim 15,wherein the openings comprise slots that extend from a distal end andterminate at a position distal to the proximal end of each percutaneousaccess device.
 17. The method of claim 12, further comprising providinga pusher mechanism adapted to advance the spinal fixation element intothe receiver head of adjacent spinal anchors.
 18. The method of claim12, further comprising providing a compression tool, and engaging atleast two adjacent percutaneous access devices to compress the devicestoward one another.
 19. The method of claim 18, wherein the compressiontool comprises first and second opposed arms that are pivotally mated toone another.
 20. The method of claim 12, further comprising providingand applying a closure mechanism to each spinal anchor to lock thespinal fixation element in the receiver heads of the anchors.